The operator of the Metro train that slammed into a stationary train in front of it apparently had activated the emergency brakes in a failed effort to stop before the accident, federal officials said yesterday as they searched for the cause of Monday's Red Line wreck that killed nine and injured 80.

Debbie Hersman of the National Transportation Safety Board said the emergency brake button, known as the "mushroom," was depressed, and the steel rails showed evidence that the brakes were engaged. Investigators also said the striking train was in automatic mode, which means onboard computers should have controlled its speed and stopped it before it got too close to the stationary train.

In addition, Metro sources said, the first two cars of that train were two months overdue for scheduled maintenance of some braking components.

Taken together, experts say these facts point to several possible scenarios: The operator activated the brakes too late; the computers that are supposed to stop a train from getting too close to another train faltered; the train's brakes failed; or some combination of those. Some passengers on the striking train have said that they never felt the train slow down.

A team of NTSB investigators painstakingly searched through the tangled heap of metal on the tracks just north of the Fort Totten Station in Northeast Washington. They were examining everything: the condition of the trains, track and signals; the actions of the operator and her downtown supervisors; and the computers that control train movement and are supposed to automatically prevent crashes. Investigators will also look at maintenance work performed this month on the computerized train control system along the stretch of track where the crash took place.

Officials began to remove the cars from the trains yesterday and plan to try to experiment with similar trains to determine approximate speed and stopping distance, Hersman said. Service on the Red Line will continue to be disrupted while the investigation proceeds.

The crash, the force of which vaulted the striking train atop the one it rammed, occurred on a curve where the speed limit is 59 mph, Hersman said. Today's experiment will also try to determine whether the curve, or anything else, obstructed the train operator's view of the stopped train. The operator, Jeanice McMillan, 42, was among those who died in the accident. Investigators will examine her cellphone and text-messaging records, review her work and rest schedule, and analyze blood samples, all standard NTSB procedures.

Investigators are also delving into the automatic train protection system, which is designed to make collisions impossible. Had the system been working correctly, it would have sensed that Train 112 was getting too close to Train 214 and directed the brakes aboard Train 112 to engage.

"I truly believe Metro is a safe system," Metro General Manager John B. Catoe Jr. said. Catoe said it was too early in the investigation to know what caused the crash, but he said there was "no evidence" that the operator was using a cellphone or texting at the time of the crash. After a special board meeting yesterday, he told reporters, "There's not a letter of evidence" to indicate operator error. And right now, he said, there is also no indication of signal failure.

The six cars that made up Train 112 were put together in an unusual way. Metro trains operate in married pairs of cars, and the lead car is almost always an "A" car, which some operators say run more smoothly and communicate better with the electronic devices buried along the track. But in the case of Train 112, the lead car was a "B" car, Metro officials said. It was unclear last night why the train was configured that way. It was also unclear what effect, if any, the configuration could have had on the crash.

The cars were among the oldest in Metro's fleet, purchased between 1974 and 1978 from Rohr Industries for the opening of the subway system. They have been rehabilitated and retrofitted "to keep them in good condition," said Metro board Chairman Jim Graham of the District.

But federal investigators consider the cars to be unsafe because of a tendency during a crash to collapse into one another like a telescope, reducing the "survivability" space, or the area in a car in which passengers can escape harm.